1. Field of the Invention
The present invention relates to a molding machine and particularly to such an improved molding machine which comprises upper and lower molding boxes into which a molding sand is shot or injected under pressure so as to form a mold and then the mold is taken out.
2. Description of the Prior Art
Conventionally, such a molding machine is constructed such that an upper molding box and a lower molding box are provided with a machine body to be close and remote from each other in vertical directions and that a match plate having molding portions is provided between the upper and lower molding boxes to be movable in lateral directions.
After the match plate is clamped between the upper and lower molding boxes, molding sand is shot by compressed air into spaces formed by the match plate and the upper and lower molding boxes, and then the molding sand in the upper and lower molding boxes is squeezed in vertical directions to firmly compact it. Then, the upper and lower molding boxes are moved away from each other in vertical directions and the match plate is taken out laterally and then the upper and lower molding boxes are moved close to each other again. Thereafter, the upper and lower molds formed in the upper and lower molding boxes are pushed down and then taken out from the machine body.
The above-mentioned sand shot is carried out by using a blowing opening formed with the side portion of each of the upper and lower molding boxes. Although the molding sand goes into the upper and lower molding boxes together with compressed air, only the compressed air is permitted to escape from the upper and lower molding boxes. For the purpose, a number of air escaping holes are formed with the inside wall of each of the upper and lower molding boxes.
However, in the above mentioned conventional art, the following problems arise in sand shot.
Namely, the molding sand with the compressed air shot into the upper and lower molding boxes, is gradually accumulated on the match plate having molding portions. The molding sand shot into the upper molding box may be easily accumulated on the upper surface of the match plate due to its weight when the compressed air is escaped from the upper molding box. Since the compressed air cannot go through the match plate having the molding portions, the compressed air must escape through the side wall of the lower molding box and a squeeze table located therebeneath. Accordingly, accumulation of the molding sand progresses on the side wall of the lower molding box and the squeeze table.
However, an air curtain may be formed on the under surface of the match plate and therefore the molding sand cannot be easily accumulated on the under surface of the molding portions of the the match plate and its accumulation cannot be precisely carried out.
Further, since the compressed air escapes from the lower molding box, the molding sand tends to fall with its weight. Therefore, it is very difficult to accumulate the molding sand on the under surface of the molding portions of the match plate. For the above reasons, molding of the lower molding box could not be done well in the conventional machine.